The present invention relates to an apparatus for reducing the transmission of vibrations from an engine to a transmission line. The apparatus includes a divided flywheel, having first and second flywheel elements. The first flywheel element is drivingly connected to the engine and the second is drivingly connected to the transmission line. The two flywheel elements are drivingly connected together by resilient means between the flywheel elements.
Such an apparatus is the subject matter of an earlier filed U.S. patent application (Ser. No. 829,508) owned in common with the present invention. An advantage of this arrangement is that a good degree of comfort can be achieved. During the resonant range of the transmission line, the flywheel elements execute comparatively large displacements relative to one another. The forces acting between the device or flywheel elements, which are transmitted via the spring mounting, exceed the strength of the frictional contact when operation takes place over a prolonged period at or near the resonant frequency. Since the drive system is designed such that the resonant frequency lies somewhat below the idling speed of the engine, a longer lasting excitation of the resonant frequency can occur in the case of repeated starting attempts. By setting the frictional contact to be relatively weak, the relative movements of the flywheel elements can be retarded, and thus damped, along a comparatively large travel distance.
However, as long as the forces transmitted between the device or flywheel elements by the spring mounting are lower than the strength of the frictional contact forces, the spring mounting cannot exert any damping effect. This is desirable for relatively small-displacement vibrations that occur between the device or flywheel elements at higher speeds of the engine and under substantially stationary operating conditions--in travel at constant speed, for example. However, there are situations in which larger relative movements between the device or flywheel elements can occur outside the resonant frequency of the drive line, such as in the load change between coasting and drive of a vehicle. Since the forces occurring in such a load change are often less than the strength of the frictional contact forces, a damping of the vibrations associated with the load change is not readily possible
It is therefore an object of the present invention to provide an apparatus of the initially-mentioned type in which the relative movements occurring between the device or flywheel elements are already effectively damped when the forces acting between the device and the flywheel elements in these relative movements are weaker than the maximum engine torque, but stronger than a predetermined threshold value.
This object and other objects are achieved by providing an apparatus of the above-described type with first and second clutches positioned between the flywheels. The second frictional clutch has frictional contact smaller than the maximum torque of the engine. In certain preferred embodiments, the first clutch is affected by clearance while the second clutch is not affected by clearance.
Consequently, the second clutch can slip even at relatively low transmitted torques until, after using up the clearance, the first clutch also slips provided the moments acting between the device or flywheel elements are adequately large, i.e. exceed the maximum engine torque. The maximum engine torque is a predetermined maximum rated engine torque for the particular engine.
Among other things, one advantage of the present invention is that unavoidable tolerances with regard to the strength of the frictional contact of the two clutches do not lead to any noticeably different behavior of the apparatus. This means that unavoidable ageing processes are also insignificant, like the divergence in production. It merely needs to be ensured that the strength of the frictional contact of the two clutches, i.e. the sum of strength of the frictional contact of the first clutch and the strength of the frictional contact of the second clutch, is greater than the maximum engine torque, while at the same time the frictional contact of the second clutch has a smaller strength than this engine torque.
According to a certain preferred embodiment of the invention, an additional third clutch is provided which is affected by clearance, to be arranged between an abutment part and the other device or flywheel element, parallel to the spring mounting. The strength of the frictional contact of this third clutch is smaller than the maximum engine torque, at least when the speeds are above the resonant frequency.
Moreover, in certain preferred embodiments, there may be provision for the second clutch and/or the third clutch to be arranged with speed-dependent frictional contact, by designing in the manner of a centrifugal clutch, for example. With this provision, the frictional contact of the second clutch can increase with increasing engine speed while the frictional contact of the third clutch can decrease with increasing engine speed. In this arrangement, the mobility given by the spring mounting between the device or flywheel elements at high speeds, at which only small vibrational amplitudes occur, is damped only slightly or not at all, while at low speed, and in particular within the resonant range at very low speed, an increased damping through friction occurs.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings, which show for purposes of illustration only, an embodiment constructed in accordance with the present invention.